Create new state before parsing FormalParameter because we don't
want to use any of the parameters as an inferred function name.

Previously the stacktrace was:
  test.js:3: Error: boom
      throw new Error('boom');
      ^
  Error: boom
      at param (test.js:3:11)
      at test.js:4:5
      at test.js:6:3

The stacktrace with this patch:
  test.js:3: Error: boom
      throw new Error('boom');
      ^
  Error: boom
      at test.js:3:11
      at test.js:4:5
      at test.js:6:3


Bug: v8:6822, v8:6513
Change-Id: Ifbadc660fc4e85248af405acd67c025f11662bd4
Reviewed-on: https://chromium-review.googlesource.com/742657Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49042}